Electrical solenoid assembly

ABSTRACT

An electrical solenoid assembly having improved long life means for determining the length of the closed state air gap of the solenoid in combination with means for increasing operating efficiency through decreasing magnetic flux fringing at pole faces.

United States Patent Chester G. Jones Kettering;

Harold D. Neal, Dayton, Ohio 863,781

Oct. 6, 1969 Apr. 6, 1971 The National Cash Registor Company Dayton, Ohio Inventors Appl. No. Filed Patented Assignee ELECTRICAL SOLENOID ASSEMBLY 5 Claims, 2 Drawing Figs.

U.S. Cl 335/279, 335/281 Int. Cl H01f 1/00 Field ofSearch 335/279, 281

[56] References Cited UNITED STATES PATENTS 2,434,096 1/1948 Ayers et al 335/281 3,150,295 9/1964 Kane et a1 335/281 9 Primary Examiner-Bernard A. Gilheany Assistant Examiner-F. E. Bell Attorneys- Louis A. Kline and John J. Callahan ABSTRACT: An electrical solenoid assembly having improved long life means for determining the length of the closed state air gap of the solenoid in combination with means for increasing operating efficiency through decreasing magnetic flux fringing at pole faces.

Patented- April 6, 1971 WITNESS INVENTORS CHESTER c. JONES a HAROLD I o. NEAL BY Q THEIR ATTORNEYS I ELECTRICALSOLENOID ASSEMBLY BACKGROUND OF THE INVENTION l Field of the Invention This invention pertains to an electrical solenoid assembly usable in business machine mechanisms and high-speedprinters and to a combination of improvements in the magnetic structure of such a solenoid.

2. Description of the Prior Art In the prior artrelatiiig to direct current solenoid structures, it is commonpractice to provide some means for preventing complete closure of the solenoid airgap. The prior art reveals many forms that such airgap maintenance structures may assume. 'These structures include projections into the airgap from either the movable armature member or the nonmovable yoke member, a stationary stop member engageable by the movable armature or some portion of the mechanism connected to the armature, and a nonmagnetic coating placed upon one or both of the s'olenoids mating pole faces.

' The present invention incorporates an airgap maintenance structure into an environment which includes means for improving the operating life of the airgap maintaining structure and means for improving the magnetic efficiency of the solenoid through the reduction of flux fringing.

SUMMARY OF THE INVENTION In the present invention, advantageous location of the airgap within the solenoid windings is combined with improvemerits to the free ends of solenoid pole portions which enable long stable pole face life and accurate determination of closed solenoid length; the resulting combination solenoid structure is applied in the business machine and high-speed printer art.

DESCRIPTION OF THE DRAWING FIG. 1 of the drawing is a detailed view of a solenoid which is constructed in accordance with the present invention.

FIG. 2 of the drawing is an overall view of a solenoid constructed in accordance with the present invention as it is used in a high-speed printer mechanism.

DESCRIITION OF THE PREFERRED EMBODIMENT FIG. 1 of the drawing shows an electrical solenoid into which the present invention is embodied, with the solenoid having omitted and cutaway portions which enable viewing of interior parts that are described in disclosing this invention. In FIG. 2 of the drawing, the solenoid shown in FIG. 1 is incorporated into a high-speed printer mechanism. The printer mechanism of FIG. 2 is composed of a movable print hammer 28 and stationary or chassis-mounted parts identified as a print hammer penetration stop assembly 55, a hammer backstop assembly 24, and the driving solenoid assembly 54. Kinetic energy from the driving solenoid is conveyed to the print hammer 28 by way of the actuating arm 17, which is connected with the solenoid armature arm 85, and thence to the solenoid armature member 86. In FIG. 2, two electrical coil members are shown in the solenoid assembly 54, while in FIG. 1 the left-hand one of these coils is omitted and the right-hand coil, identified as 91, is shown cutaway.

In FIG. 1, the solenoid assembly 54 is shown to have a stationary mounted frame portion 94, which is connected to two salient or externally protruding pole portions; the number 92 identifies the left-hand one of these stationary salient pole portions. In FIG. 2, the movable armature portion of the solenoid is identified by the number 86, the armature connecting arm by the number 85, and the left-hand movable armature pole portion by the number 112.

Also identified in FIG. 1 is the path traversed by the solenoids magnetic flux 87; it is to be noted that the major flux path 87 is circular in nature and threads only the pole region of the solenoid and does not to a significant degree enter the region near the solenoid pivot portion 43.

In FIG. 1, the left-hand stationary salient pole portion 92 is shown cut away at the break line 106 in order that the structure adjacent to the pole face 101 may be clearly shown. Above the break line 106, there is shown a region 107, which is composed of a magnetic material suchas ferrous metal'and represent the composition used throughout the solenoid frame portion 94. Between the region 107 and the pole face 101 there are shown two discrete layers of material, which differ in composition from that of the region 107. The first of these layers, 108, is adjacent to the ferrous metal of the region 107 and attached thereto, while the second of these layers, 109, has the pole face 101 on one side and has an attachment with the layer 108 on the other side. I

The armature pole portion 112 in FIG. 1 is shown to also have two discrete layers of material immediately adjacent to its pole face 99. The first of these armature pole portion layers, the layer adjacent to the armature ferrous material, is identified by the numeral 111, while the second, or outermost, of the armature layers is identified by the numeral 110i In FIG. 1, the layers associated with the armature pole portion 112 are shown in noncutaway fashion. The layers associated with both armature and stationary poles are shown in noncutaway fashion for the poles located within the electrical coil member 91. All of the layers on each of the pole portions are shown exaggerated in size in order that they may be clearly visible in FIG. 1.

Between the stationary pole face 101 and the the movable or armature pole face 99 in FIG. 1, there is shown an airgap region 93; this airgap region is also identified as 93 between the pole faces'shown inside the electrical coil member 91. This airgap'is relatively large when the solenoid is in the open position, as shown in FIG. 1; upon excitation of the electrical coil members, such as 91, the armature 86 moves toward the solenoidframe member 94, and the air gap 93 is reduced to a small, or near zero, length.

In operating the solenoid shown in FIGS. 1 and 2, it is desirable to maintain some airgap or nonmagnetic gap between armature pole portions such as 112 and stationary pole portions such as 92 when the solenoid is in the closed position; it is found that this airgap greatly reduces the attraction between solenoid pole portions resulting from permanent or residual magnetism in frame and armature members. This reduction of residual magnetic attraction provides faster more uniformly controllable relaxation of the armature pole portions away from the stationary pole portions upon deenergization of the electrical coils.

To improve the operating life of the solenoid and other parts of the printer mechanism shown in FIG. 2 of the drawing, it has been found desirable to employ a nonrigid coupling between armature and armature arm members. Since this nonrigid coupling yields to a certain degree during solenoid closure, the airgap-determining structure for the solenoid must be located at the solenoid pole faces and be independent of the solenoid output member. To this end, it has been found desirable to especially prepare the faces 99 and 101 of the mating magnetic pole portions so that the faces may meet during closure of the solenoid while yet providing a nonmagnetic gap between armature and frame pole portions. In contemplating such pole face preparation, it is necessary to realize that these faces are also subjected to repeated impacting as armature pole portion meets yoke pole portion at the completion of a solenoid stroke. The force with which this impact occurs is determined by both the magnetic attraction between armature and yoke pole portions and by the inertia or kinetic energy which is stored in the armature and associated moving parts by virtue of their being masses in motion. It is notable that the magnetic component of this force has the greatest magnitude that it ever reaches during this impact, since the solenoid is, at the instant of impact, operating with a minimal airgap.

From an energy viewpoint, satisfactory operation of a solenoid requires that the armature and yoke pole portions and pole faces must be capable of dissipating a large portion of the energy which has been transferred from solenoid to solenoid actuated mass each time the driven'mechanism goes through an operating cycle; this dissipation occurs primarily through heating of the pole portion material and through sound radiation from the solenoid structure upon impact.

In order that the solenoid pole portions have faces which are capable of both enduring repeated impact loading and capable of assuring thata stable and predictable length of nonmagnetic gap is maintained between closed pole portions over a long operating life for the mechanism, it has been found necessary to especially prepare the structure upon which the pole faces, such as those at 99 and 101, are mounted during solenoid manufacture. This preparation includes the placing of two layers of material between the pole portion material and the pole face.

Tungsten carbide material is hard and nonmagnetic in nature and has been found suitable for forming the nonmagnetic gap desired between armature and yoke pole portions in the present invention. In order that the hardness of the tungsten carbide not be detrimental to its life in this application and that cracking or shattering of the tungsten carbide layer not occur, it has been found desirable to intersperse a layer of backing material between the relatively hard tungsten carbide and the relatively soft magnetic steel of the solenoid pole portion. In the present solenoid, it has been found that alayer of carbon steel which has a hardness intermediate that of the tungsten carbide and the magnetic iron is satisfactory for this backing layer.

The conventional technique of case hardening or carburizing has been found satisfactory for placing this layer of carbon steel on the pole portion. In the process used for the mechanism of FlGS. 1 and 2, the face end of the pole portion is first hardened to a value near 62, or file hardness," on the Rockwell scale and is subsequently drawn to a hardness between 50 and 56. Carbon imparted during the initial hardening is caused to extend to a depth of 0.015 to 0.025 inch into the pole portion, and then up to 0.003 inch of this hardened material is removed by grinding.

Following the case hardening of the pole portion face ends, a layer of tungsten carbide having a thickness between 0.0015 and 0.00225 inch is added to the face end of the pole portion by means of an explosive detonation process which is known in the art. It has been found that the case hardening operation provides a region of sufiicient hardness and durability for resisting impact loads so that the tungsten carbide coating will not fail under the repeated impacts of solenoid closure. In this construction, it is of course the tungsten carbide layer at both magnetic faces of the solenoid, both faces 99 and 101 in FlG. l, which provides a nonmagnetic gap; an effective gap of 0.003 to 0.0045 inch at each pole mating is provided by the two layers; or a gap of 0.006 to 0.009 inch for the complete circular magnetic path illustrated. It is clear that tungsten carbide need not be applied to both the movable and nonmovable pole portions in HO. 1; some embodiments of the invention may have need of restricting this coating to a single pole portion. Generally, however, it is found desirable to locate at least a carburized or case hardened layer beneath the pole face of each pole portion in order that long operating life may be obtained.

ln a well-designed high-speed printer, there is need for compact mounting of mechanism parts into a small space in order that the printer package be small and in order that high-density printing upon the output media be possible.

In a high-density printing mechanism, it is desirable to convert electrical energy into kinetic or motional energy with efficiency as high as possible in order that the needed kinetic energy be developed with the lowest possible input of electrical energy. The advantages of a low electrical input for a printer are apparent if it be considered that ultimately almost all the energy received by a printer must be conveyed away from the mechanism in the form of rejected heat. Dissipation of this energy in the form of heat requires that elaborate consideration be given to mechanism layout and to ventilation In the present invention, it has been found that one avenue by which energy input to the printer may be reduced and this heat transfer problem minimized is through increasing the efficiency with which the actuating solenoid converts applied electrical energy into useful active magnetic flux.

It is well known in the electromagnetic art that the magnetic flux emanating from an isolated magnetic pole structure tends to form a pattern having a plurality of concentric circles which intersect the originating pole structure over the surface of the pole structure but in an especially high concentration at the outer edges and corners of the pole structure. In similar fashion, it is also known that between two magnetic pole portions which are separated by an airgap, as is the situation at 93 in the solenoid of FIG. 1, the flux which links the two pole portions will concentrate at the outer edges and corners of the pole portions, and much of the flux will traverse a path between pole portions which is circular in nature and lies outside the immediate space between pole portions. Since the flux which travels outside the space between magnetic pole portions must travel in a medium of low magnetic permeabilitynamely, air-and this flux travels over a path which is long in comparison to space between the pole portions, this flux is less effective in producing attractive force between the pole portions than it would be if confined to the immediate region between pole portions.

It has been found that one way to reduce the tendency of the magnetic flux to travel in paths lying outside the space between pole portionsthat is, to reduce the fringing effect of the fluxcomprises placing the airgap separating the magnetic pole portions within the length of the electrical coil which generates the magnetic flux. When the airgap separating pole portions is located in this position, the solenoid effect or the rigid and orderly orientation of flux within the electrical coil is effective to confine the interpole flux to a desirable path largely existing only from pole portion to pole portion across the airgap.

ln FIG. 1 of the drawing, the electrical solenoid for the present invention is shown with the airgap located well within the electrical coil in accordance with the above technique for reducing flux fringing. It has been found that it is not necessary to locate the airgap in the center of the solenoid, as is indicated in FlG. 1, but that substantial reduction of fringing occurs if the gap is placed at a point located even one-fifth of the distance along the electrical coil length for the embodiment shown. This latter placement for the gap, wherein a larger percentage of the magnetic iron existing within the electrical coil is attached to the stationary, or frame, portion of the solenoid, as opposed to being attached to the movable armature portion, has distinct advantages when the amount of iron material which the solenoid must accelerate is considered. This latter location, wherein the gap is located near the top of the solenoid, also offers advantages from the viewpoint of how deep into a solenoid it is necessary to reach for cleaning dust and debris from the solenoid during maintenance operations on the solenoid mechanism. In practice, it is found that a compromise, or trade-off, is desirable between the benefits of flux fringe reduction and the disadvantage of having the airgap near the exact center of the electrical coil.

In a practical printer embodiment, it is found that an actuating solenoid which employs the flux fringing reduction technique of locating solenoid airgap within the electrical coil should also employ the multiple layers of hard material beneath the pole faces, as described earlier in this specification, in order that the pole faces which are so inaccessible for maintenance and inspection provide satisfactory operation over the long life of the solenoid and in order that the greater flux utilization efficiency not degrade the solenoid release characteristics.

In the mechanism shown in FIGS. 1 and 2 of the drawing, where the location of the airgap within the electrical coil is min-N (I710 embodied into the solenoid, it is apparent that the travel which is permitted for the solenoid armature is small enough to prevent the armature pole face 99 from ever emerging from the electrical coil. This condition is typical of low fringing solenoids which are embodied into high-performance fast-acting mechanisms'ln an environment where it is physically impossible to view the solenoid pole faces, the importance of pole face surfaces which are reliable and predictable as to physical and magnetic properties over a long period of operation is apparent; clearly, if the pole faces 99 and 101 in FIG. 1 are subject to dimensional change and to sloughing off of particles from the poles, performance of the solenoid is adversely affected. Especially when the gap over which the solenoid armature moves measures but a few thousandths of an inch and is inaccessible for either inspection or cleaning without disassembly of the mechanism, the reliability and predictability of the pole faces which result from the previously-described preparation are important.

We claim:

1. An electrical solenoid assembly comprising:

a solenoid frame member having one or more salient magnetic pole portions, at least one of which is surrounded by an electrical coil'member capable of inducing magnetic flux into said pole portions and said frame member;

a magnetically conductive armature member having one or more salient magnetic pole portions engageable by said frame pole portions in mating fashion upon energization of said electrical coil member;

a pair of discrete layers of inorganic material affixed to each of said frame pole and said armature pole portions in the pole face region where said pole portions come into engagement upon excitation of said electrical coil member;

the first of said layers, a layer located immediately adjacent to material composing each of said yoke frame and armature pole portions, being composed of material which is magnetic and relatively hard with respect to material in said frame and armature pole portions and being of a size which substantially covers the pole face region;

the second of said layers, the layer most external to said frame and armature pole portions and contactable by a similar layer on said mating pole portion, being composed of a controlled thickness of material which is nonmagnetic, impact-resistant, dimensionally stable under impact loading and harder than material in said first layer, and of a size which substantially covers the pole face region;

whereby said solenoid pole face regions are provided with precise and stable means for determining minimum nonmagnetic gap space between engaged movable and stationary pole portions and are provided with long life low maintenance mating surfaces which can be practically mounted in an inaccessible region of said solenoid assembly;

said cngageablepole portions of said frame and armature members having a total length which is approximately equal to the total length of said electrical coil member;

whereby said electrical coil member approximately covers said pole portions when they are engaged in a mating position upon energization of said electrical coil member;

said armature pole portions having an individual length which is less than one-half of said total length but is of substantial and greater than zero length; and

whereby said pole portions have their mating pole face regions located well within the length of said electrical coil during engagement where magnetic flux fringe effect from said pole portions is minimized and said long life mating surfaces afford useful unattended service.

2. An electrical solenoid assembly as in claim 1 wherein:

said first discrete inorganic layer is composed of case hardened steel; and

said second discrete inorganic layer is composed of tungsten carbide material attached to said first discrete inorganic layer.

3. An electrical solenoid assembly as in claim 2 wherein: said case hardened steel layer has a thickness near 0.017

5. A direct current electrical solenoid assembly for energizing a high-speed printing mechanism, comprising:

a solenoid frame member composed of ferrous magnetic material and rigidly mounted upon a chassis portion of said printing mechanism, said frame member having a pair of integral salient magnetic pole portions, with one end of each of said pole portions providing a pole face;

a pair of electrical coil members each mounted upon one of said magnetic pole portions so as to induce magnetic flux into said pole portions and said frame upon being electriv cally energized;

a magnetically conductive armature member connected with a print hammer exciting arm portion of said printing mechanism and also having a pair of integral salient magnetic pole portions, one end of each of said pole portions providing a pole face, said pole faces being engageable by one of said'pole faces of said frame pole portions in mating fashion upon energization of said coil members;

a carbon-impregnated hardened layer of magnetic steel material located at the pole face of each of said magnetic pole portions and composing the face terminal of said pole portionss structural material, said carbon-impregnated layer being of a predetermined minimum thickness and of a size which substantially covers said pole portions face region;

a layer of tungsten carbide material located upon said carbon-impregnated layer of at least one of said magnetic pole portions in each engageable pair; said tungsten carbide layer having a smooth external surface, a predetermined thickness suitable for closed solenoid gap determination, and a lateral extent covering at least a major portion of said pole face;

each engageable mating pole portion having a total length which is equal to or slightly greater than the external length of said electrical coil member; said frame pole portion of each of said pole portion pairs having a length which is greater than one-half of said total length but less than four-fifths of said total length; and

a length for said armature pole portion of each of said pole portion pairs having a length which is less than one half of said total length but greater than one fifth of said total length whereby said solenoids pole faces meet well within the length of said electrical coils in a location where magnetic flux fringing is minimized and solenoid efiiciency is thereby increased and said meeting location is made practical and useful by way of said electrical solenoid having an accurately determined closed position nonmagnetic gap which is maintainable with minimum adjustment and maintenance to said pole faces over a long operating life. 

1. An electrical solenoid assembly comprising: a solenoid frame member having one or more salient magnetic pole portions, at least one of which is surrounded by an electrical coil member capable of inducing magnetic flux into said pole portions and said frame member; a magnetically conductive armature member having one or more salient magnetic pole portions engageable by said frame pole portions in mating fashion upon energization of said electrical coil member; a pair of discrete layers of inorganic material affixed to each of said frame pole and said armature pole portions in the pole face region where said pole portions come into engagement upon excitation of said electrical coil member; the first of said layers, a layer located immediately adjacent to material composing each of said yoke frame and armature pole portions, being composed of material which is magnetic and relatively hard with respect to material in said frame and armature pole portions and being of a size which substantially covers the pole face region; the second of said layers, the layer most external to said frame and armature pole portions and contactable by a similar layer on said mating pole portion, being composed of a controlled thickness of material which is nonmagnetic, impact-resistant, dimensionally stable under impact loading and harder than material in said first layer, and of a size which substantially covers the pole face region; whereby said solenoid pole face regions are provided with precise and stable means for determining minimum nonmagnetic gap space bEtween engaged movable and stationary pole portions and are provided with long life low maintenance mating surfaces which can be practically mounted in an inaccessible region of said solenoid assembly; said engageable pole portions of said frame and armature members having a total length which is approximately equal to the total length of said electrical coil member; whereby said electrical coil member approximately covers said pole portions when they are engaged in a mating position upon energization of said electrical coil member; said armature pole portions having an individual length which is less than one-half of said total length but is of substantial and greater than zero length; and whereby said pole portions have their mating pole face regions located well within the length of said electrical coil during engagement where magnetic flux fringe effect from said pole portions is minimized and said long life mating surfaces afford useful unattended service.
 2. An electrical solenoid assembly as in claim 1 wherein: said first discrete inorganic layer is composed of case hardened steel; and said second discrete inorganic layer is composed of tungsten carbide material attached to said first discrete inorganic layer.
 3. An electrical solenoid assembly as in claim 2 wherein: said case hardened steel layer has a thickness near 0.017 inch and a Rockwell hardness near 53; and said tungsten carbide layer has a thickness near 0.0019 inch.
 4. An electrical solenoid assembly as in claim 1 wherein said pole portion of said armature member has a length greater than one-fifth the length of said pole portion of said frame member but less than one times the length of said frame member pole portion, said armature member pole portion thereby being greater than one-tenth the length of said electrical coil member but less than one-half the length of said electrical coil member.
 5. A direct current electrical solenoid assembly for energizing a high-speed printing mechanism, comprising: a solenoid frame member composed of ferrous magnetic material and rigidly mounted upon a chassis portion of said printing mechanism, said frame member having a pair of integral salient magnetic pole portions, with one end of each of said pole portions providing a pole face; a pair of electrical coil members each mounted upon one of said magnetic pole portions so as to induce magnetic flux into said pole portions and said frame upon being electrically energized; a magnetically conductive armature member connected with a print hammer exciting arm portion of said printing mechanism and also having a pair of integral salient magnetic pole portions, one end of each of said pole portions providing a pole face, said pole faces being engageable by one of said pole faces of said frame pole portions in mating fashion upon energization of said coil members; a carbon-impregnated hardened layer of magnetic steel material located at the pole face of each of said magnetic pole portions and composing the face terminal of said pole portions''s structural material, said carbon-impregnated layer being of a predetermined minimum thickness and of a size which substantially covers said pole portion''s face region; a layer of tungsten carbide material located upon said carbon-impregnated layer of at least one of said magnetic pole portions in each engageable pair; said tungsten carbide layer having a smooth external surface, a predetermined thickness suitable for closed solenoid gap determination, and a lateral extent covering at least a major portion of said pole face; each engageable mating pole portion having a total length which is equal to or slightly greater than the external length of said electrical coil member; said frame pole portion of each of said pole portion pairs having a length which is greater than one-half of said total length but less than four-fifths of said total length; and a length for said arMature pole portion of each of said pole portion pairs having a length which is less than one half of said total length but greater than one fifth of said total length whereby said solenoid''s pole faces meet well within the length of said electrical coils in a location where magnetic flux fringing is minimized and solenoid efficiency is thereby increased and said meeting location is made practical and useful by way of said electrical solenoid having an accurately determined closed position nonmagnetic gap which is maintainable with minimum adjustment and maintenance to said pole faces over a long operating life. 